Patterning of high refractive index glasses by plasma etching

ABSTRACT

Plasma etching processes for forming patterns in high refractive index glass substrates, such as for use as waveguides, are provided herein. The substrates may be formed of glass having a refractive index of greater than or equal to about 1.65 and having less than about 50 wt % SiO 2 . The plasma etching processes may include both chemical and physical etching components. In some embodiments, the plasma etching processes can include forming a patterned mask layer on at least a portion of the high refractive index glass substrate and exposing the mask layer and high refractive index glass substrate to a plasma to remove high refractive index glass from the exposed portions of the substrate. Any remaining mask layer is subsequently removed from the high refractive index glass substrate. The removal of the glass forms a desired patterned structure, such as a diffractive grating, in the high refractive index glass substrate.

PRIORITY CLAIM

This application claims the benefit of priority under 35 U.S.C. § 119(e)of U.S. Provisional Application No. 62/442,809, filed on Jan. 5, 2017,the entire disclosure of which is incorporated herein by reference.

INCORPORATION BY REFERENCE

This application incorporates by reference the entirety of each of thefollowing patent applications: U.S. application Ser. No. 14/555,585filed on Nov. 27, 2014, published on Jul. 23, 2015 as U.S. PublicationNo. 2015/0205126; U.S. application Ser. No. 14/690,401 filed on Apr. 18,2015, published on Oct. 22, 2015 as U.S. Publication No. 2015/0302652;U.S. application Ser. No. 14/212,961 filed on Mar. 14, 2014, now U.S.Pat. No. 9,417,452 issued on Aug. 16, 2016; and U.S. application Ser.No. 14/331,218 filed on Jul. 14, 2014, published on Oct. 29, 2015 asU.S. Publication No. 2015/0309263.

BACKGROUND

Field

The present disclosure relates to display systems and, more particularlyto high resolution patterning of high refractive index glasses for usetherein.

Description of the Related Art

Modern computing and display technologies have facilitated thedevelopment of systems for so called “virtual reality” or “augmentedreality” experiences, in which digitally reproduced images or portionsthereof are presented to a user in a manner wherein they seem to be, ormay be perceived as, real. A virtual reality, or “VR”, scenariotypically involves the presentation of digital or virtual imageinformation without transparency to other actual real-world visualinput; an augmented reality, or “AR”, scenario typically involvespresentation of digital or virtual image information as an augmentationto visualization of the actual world around the user. A mixed reality,or “MR”, scenario is a type of AR scenario and typically involvesvirtual objects that are integrated into, and responsive to, the naturalworld. For example, an MR scenario may include AR image content thatappears to be blocked by or is otherwise perceived to interact withobjects in the real world.

Referring to FIG. 1, an augmented reality scene 1 is depicted. The userof an AR technology sees a real-world park-like setting 1100 featuringpeople, trees, buildings in the background, and a concrete platform1120. The user also perceives that he “sees” “virtual content” such as arobot statue 1110 standing upon the real-world platform 1120, and aflying cartoon-like avatar character 1130 which seems to be apersonification of a bumble bee. These elements 1130, 1110 are “virtual”in that they do not exist in the real world. Because the human visualperception system is complex, it is challenging to produce AR technologythat facilitates a comfortable, natural-feeling, rich presentation ofvirtual image elements amongst other virtual or real-world imageryelements.

Systems and methods disclosed herein address various challenges relatedto AR and VR technology.

SUMMARY

According to some aspects, methods are disclosed for forming one or morediffractive gratings in a waveguide. In some embodiments, a method maycomprise providing a waveguide having a refractive index of greater thanor equal to about 1.65. In some embodiments, more than 50 wt % of thewaveguide is formed of one or more of B₂O₃, Al₂O₃, ZrO₂, Li₂O, Na₂O,K₂O, MgO, CaO, SrO, BaO, ZnO, La₂O₃, Nb₂O₅, TiO₂, HfO, and Sb₂O₃. Insome embodiments, the method may further comprise providing a mask layerover the waveguide, the mask layer having a pattern corresponding to theone or more diffractive gratings, the pattern selectively exposingportions of the waveguide, and anisotropically etching the exposedportions of the waveguide to define the one or more diffractive gratingsin the waveguide.

In some embodiments, providing a mask layer comprises providing thepattern comprising a first diffraction grating pattern over a firstregion and a second diffraction grating pattern in the second region ofthe waveguide, wherein the second region extends over a majority of anarea of a surface of the waveguide. In some embodiments, the firstdiffraction grating pattern corresponds to an incoupling optical elementand the second diffraction grating pattern corresponds to an outcouplingoptical element. In some embodiments, providing a mask layer comprisesproviding the pattern comprising a third diffraction grating patternover a third region of the waveguide, wherein the third diffractiongrating pattern corresponds to an orthogonal pupil expander configuredto redirect light from the incoupling optical element to the topcoupling optical. In some embodiments, the one or more diffractivegratings comprise substantially parallel lines, wherein each line has acritical dimension of less than about 1 micron and an aspect ratio ofbetween about 1:10 to about 10:1. In some embodiments, each line has acritical dimension of less than about 300 nm.

According to some aspects plasma etching processes for forming featuresin a high refractive index glass substrate are provided. In someembodiments, the process may comprise providing a patterned mask layeron at least a portion of the high refractive index glass substrate, thesubstrate formed of glass having a refractive index of greater than orequal to about 1.65 and comprising less than about 50 wt % SiO₂, andetching the features in the substrate by exposing the mask layer andhigh refractive index glass substrate to a plasma etch comprisingchemical and physical etchant species to selectively remove exposed highrefractive index glass from the high refractive index glass substrate.

In some embodiments, the high refractive index glass substrate comprisesless than about 30 wt % SiO₂. In some embodiments, more than 50 wt % ofthe high refractive index glass substrate is formed of one or more ofB₂O₃, Al₂O₃, ZrO₂, Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, ZnO, La₂O₃,Nb₂O₅, TiO₂, HfO, and Sb₂O₃. In some embodiments, the high refractiveindex glass substrate has a refractive index of greater than or equal toabout 1.70. In some embodiments, exposing the mask layer and highrefractive index glass substrate to a plasma etch comprisesanisotropically removing high refractive index glass from an exposedsurface of the high refractive index glass substrate.

In some embodiments, the plasma is generated in situ in a reactionchamber accommodating the high refractive index glass substrate. In someembodiments, the source gas comprises SF₆ and Ar gas. In someembodiments, the source gas comprises BCl₃, HBr, and Ar gas. In someembodiments, the source gas comprises CF₄, CHF₃, and Ar gas. In someembodiments, the reaction chamber is the reaction chamber of aninductively coupled plasma (ICP) reactor. In some embodiments, thereaction chamber is the reaction chamber of a dual frequency ICPreactor. In some embodiments, each of the features has a criticaldimension of less than about 100 nm. In some embodiments, each of thefeatures has an aspect ratio of between about 1:10 to about 10:1. Insome embodiments, the features are sized and spaced to form adiffractive grating. In some embodiments, the mask layer comprises apolymeric resist layer. In some embodiments, the process may furthercomprise removing remaining mask layer from the high refractive indexglass substrate after exposing the mask layer and high refractive indexglass substrate to the plasma.

According to some aspects, processes for forming features in a highrefractive index glass substrate are provided. In some embodiments, theprocess may comprise selectively exposing a portion of the highrefractive index glass substrate to a plasma in a reaction chamber toselectively remove high refractive index glass from the high refractiveindex glass substrate, wherein the high refractive index glass substratecomprises less than about 50 wt % SiO₂ and has a refractive index ofgreater than or equal to about 1.65.

In some embodiments, high refractive index glass substrate comprises oneor more of B₂O₃, Al₂O₃, ZrO₂, Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, ZnO,La₂O₃, Nb₂O₅, TiO₂, HfO, and Sb₂O₃. In some embodiments, selectivelyexposing a portion of the high refractive index glass substrate definesa pattern of protrusions in the substrate, wherein the protrusions forman optical diffraction grating. In some embodiments, the process mayfurther comprise depositing a mask layer on the substrate, patterningthe mask layer to define a first set of spaced apart lines in a firstregion over the substrate, and a second set of spaced part lines in asecond region over the substrate, wherein selectively exposing a portionof the high refractive index glass substrate comprises etching thesubstrate through the mask layer to form a light incoupling diffractivegrating in an area of the substrate corresponding to the first region,and a light outcoupling diffractive grating in an area of the substratecorresponding to the second region. In some embodiments, patterning themask layer further defines a third set of spaced apart lines in a thirdregion over the substrate, and wherein selectively exposing a portion ofthe high refractive index glass substrate comprises etching thesubstrate through the mask layer to form an orthogonal pupil expandercorresponding to the third region.

According to some other aspects, methods for forming an opticalwaveguide structure are provided. The methods comprise identifyingdesired dimensional characteristics of first features to be formed in ahigh-index glass substrate and identifying etching characteristics of anetching process that is used for forming at least the first features inthe high-index glass substrate. Based on the identified etchingcharacteristics, biased dimensional characteristics are determined forsecond features of a patterned layer that are to be formed on thehigh-index glass substrate prior to forming the first features in thehigh-index glass substrate. The patterned layer is formed on thehigh-index glass substrate. Forming the patterned layer includes formingthe second features in the patterned layered, the second features havingthe biased dimensional characteristics. The methods also comprisetransferring, using the etching process, a pattern of the secondfeatures, having the biased dimensional characteristics, into thehigh-index glass to form the first features, having the desireddimensional characteristics in the high-index glass substrate.

According to yet other aspects, methods are provided for patterning aglass substrate. The methods comprise providing an etch mask over aglass substrate formed of glass having a refractive index of 1.65 orgreater. Features in the etch mask for defining corresponding featuresin the glass substrate are larger than a desired size of thecorresponding features. The methods also comprise etching the glasssubstrate through the etch mask to define the features in the glasssubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a user's view of augmented reality (AR) through an ARdevice.

FIG. 2 illustrates an example of wearable display system.

FIG. 3 illustrates a conventional display system for simulatingthree-dimensional imagery for a user.

FIG. 4 illustrates aspects of an approach for simulatingthree-dimensional imagery using multiple depth planes.

FIGS. 5A-5C illustrate relationships between radius of curvature andfocal radius.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user.

FIG. 7 illustrates an example of exit beams outputted by a waveguide.

FIG. 8 illustrates an example of a stacked waveguide assembly in whicheach depth plane includes images formed using multiple differentcomponent colors.

FIG. 9A illustrates a cross-sectional side view of an example of a setof stacked waveguides that each includes an incoupling optical element.

FIG. 9B illustrates a perspective view of an example of the plurality ofstacked waveguides of FIG. 9A.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B.

FIG. 10 is a process flow diagram for an example of a plasma etchingprocess according to some embodiments.

FIG. 11A illustrates a cross-sectional side view of an example of aglass substrate having an overlying etch mask.

FIG. 11B illustrates a cross-sectional side view of an example of thestructure of FIG. 11A undergoing a directional etch.

FIG. 11C illustrates a cross-sectional side view of an example of thestructure of FIG. 11B after etching the glass substrate and removing theoverlying etch mask.

FIG. 12A illustrates a cross-sectional side view of another example ofan etch mask overlying a glass substrate.

FIG. 12B illustrates a cross-sectional side view of an example of thestructure of FIG. 12A after expanding the sizes of features of the etchmask.

FIG. 12C illustrates a cross-sectional side view of an example of thestructure of FIG. 12B undergoing a directional etch.

FIG. 12D illustrates a cross-sectional side view of an example of thestructure of FIG. 12B after etching the glass substrate and removing theoverlying etch mask.

The drawings are provided to illustrate example embodiments describedherein and are not intended to limit the scope of the disclosure. Thedrawings are not necessarily drawn to scale.

DETAILED DESCRIPTION

VR and AR display systems may utilize high refractive index glasssubstrates as waveguides for providing image information in the form oflight to a user. The high refractive index of the substrates providesdesirable optical properties, including allowing the output of lightfrom the substrate at a wide range of angles and facilitating totalinternal reflection (TIR) of light within that substrate. It will beappreciated that optical elements may be provided on the surface of thesubstrate to, e.g., incouple light for TIR within the substrate and/oroutcouple light to the user. As an example, these optical elements maytake the form of diffractive gratings.

It is difficult, however, to etch optical elements such as diffractivegratings directly in the body of high refractive index glass substrates.Substrate materials having a high refractive index are challenging toetch, particularly at the dimensions desired for optical elements, dueto the low amounts of silicon oxide in the substrates. The opticalproperties of the optical elements, however, are highly dependent uponthe regularity, dimensions, and shapes of the elements. It has beenfound that typical wet chemical etching or reactive ion etching haveinsufficiently high resolution and/or do not form features withsufficiently vertical or straight sidewalls and/or sufficient aspectratios for use as optical diffractive gratings.

Consequently, a conventional approach for forming such optical elementsis to deposit material for forming optical elements on the substrates.For example, the material may be vapor deposited and patterned. Asanother example, the optical elements may be formed in a separate filmthat is attached to the substrate. Such deposition or attachment,however, may undesirably add manufacturing complications and may alsointroduce optical artifacts. For example, the interfaces between thesubstrate and the deposited layer or film, and any adhesive layersjoining the film to the substrate, may cause reflections that in turncause optical artifacts.

According to some embodiments, an etching process allows features to beformed directly in the body of a high refractive index glass substrate,while providing high resolution and selectivity. In some embodiments,the etching process is a plasma etching process that comprises forming apatterned mask layer on at least a portion of the surface of the highrefractive index glass substrate, and exposing the mask layer and highrefractive index glass substrate to a plasma in a reaction chamber toremove a desired amount of high refractive index glass from the exposedportions of the surface of the substrate. The removal leaves features orstructures having a desired pattern. The features may form, for example,optical elements such as diffractive gratings, on the surface of thehigh refractive index glass substrate. In some embodiments, anyremaining mask layer of material may be removed from the surface of thesubstrate.

Preferably, the high refractive index glass substrate has a refractiveindex of about 1.65 or more or 1.75 or more, and less than about 50 wt %SiO₂. In some embodiments, more than 50 wt % of the substrate is formedof one or more of B₂O₃, Al₂O₃, ZrO₂, Li₂O, Na₂O, K₂O, MgO, CaO, SrO,BaO, ZnO, La₂O₃, Nb₂O₅, TiO₂, HfO, and Sb₂O₃. In some embodiments, theplasma etch is performed using a very high frequency (VHF) inductivelycoupled plasma (ICP). In some embodiments, the VHF power is in a rangeof 10]-2500 W and RF power is in a range of 10-500 W. Preferably, theetching process includes both chemical and physical etching components.In some embodiments, the etch chemistry includes one or morehalogen-containing compounds and one or more inert gases. Examples ofhalogen-containing compounds include CF₄, CHF₃, SF₆, O₂, Cl₂, BCl₃, andHBr and examples of inert gases include Ar, He, and N₂. The plasma maybe performed at a temperature in the range of −150-50° C.

In some embodiments, features having critical dimensions of about 10-500nm, including about 10-100 nm, may be etched in the high refractiveindex glass substrates and may have aspect ratios in the range of about1:10 to about 10:1. In addition, the etched features may havesubstantially straight sidewalls. In some embodiments, these featuresmay be utilized in a variety of applications, such as in opticalapplications, including as waveguides for VR and AR display systems. Forexample, the etched features may form incoupling optical elements,outcoupling optical elements, or light distribution elements. In someembodiments, the plasma etching processes may be utilized to etch anarbitrary desired patterned into a high refractive index glass substratefor other applications where high resolution patterning is desired.

Advantageously, plasma etching processes according to some embodimentsallow high resolution patterning and etching of high refractive indexglass substrates to form features directly in the body of thesubstrates. The ability to directly etch the substrates may simplify themanufacturer of devices utilizing such features by obviating the need toseparately form and attach films containing the features to thesubstrate. In some embodiments, optical performance may be improved byeliminating the presence of interfaces formed by the separately attachfilms.

In some embodiments, the etch mask used for patterning the underlyinghigh refractive index glass substrate may be biased with etch maskfeatures having dimensional characteristics that compensate for thecharacteristics of the etch used to etch the pattern into the substrate.For example, the sizes of features in the etch mask may be larger (e.g.,wider and/or taller) than the desired sizes of features to be etchedinto the substrate, thereby compensating for etching of the etch maskitself over the course of etching the substrate such that, even withetching of the mask itself, the features formed in the substrate are ofa desired size. In some embodiments, features in the etch mask may bepatterned with sizes larger than the desired sizes of features in thesubstrate. In some other embodiments, the sizes of the features in theetch mask may be increased by depositing a layer of material to augmentthose features and/or by chemically reacting those features to increasetheir sizes. In some embodiments, the substrate may be patterned throughthe etch mask using a plasma-based etch as disclosed herein. In someother embodiments, the substrate may be patterned using ion beammilling. Advantageously, the biased etch mask facilitates the rapidpatterning of high refractive index glass substrates while preciselyforming features of desired dimensions.

Reference will now be made to the drawings, in which like referencenumerals refer to like features throughout.

Example Display Systems

FIG. 2 illustrates an example of wearable display system 80 into whichthe etched high refractive index glass substrates may be incorporated.The display system 80 includes a display 62, and various mechanical andelectronic modules and systems to support the functioning of thatdisplay 62. The display 62 may be coupled to a frame 64, which iswearable by a display system user or viewer 60 and which is configuredto position the display 62 in front of the eyes of the user 60. Thedisplay 62 may be considered eyewear in some embodiments. In someembodiments, a speaker 66 is coupled to the frame 64 and positionedadjacent the ear canal of the user 60 (another speaker, not shown, mayoptionally be positioned adjacent the other ear canal of the user toprovide for stereo/shapeable sound control). The display system may alsoinclude one or more microphones 67 or other devices to detect sound. Insome embodiments, the microphone is configured to allow the user toprovide inputs or commands to the system 80 (e.g., the selection ofvoice menu commands, natural language questions, etc.) and/or may allowaudio communication with other persons (e.g., with other users ofsimilar display systems).

With continued reference to FIG. 2, the display 62 is operativelycoupled by communications link 68, such as by a wired lead or wirelessconnectivity, to a local data processing module 70 which may be mountedin a variety of configurations, such as fixedly attached to the frame64, fixedly attached to a helmet or hat worn by the user, embedded inheadphones, or otherwise removably attached to the user 60 (e.g., in abackpack-style configuration, in a belt-coupling style configuration).The local processing and data module 70 may comprise a hardwareprocessor, as well as digital memory, such as non-volatile memory (e.g.,flash memory or hard disk drives), both of which may be utilized toassist in the processing, caching, and storage of data. The data includedata a) captured from sensors (which may be, e.g., operatively coupledto the frame 64 or otherwise attached to the user 60), such as imagecapture devices (such as cameras), microphones, inertial measurementunits, accelerometers, compasses, GPS units, radio devices, gyros,and/or other sensors disclosed herein; and/or b) acquired and/orprocessed using remote processing module 72 and/or remote datarepository 74 (including data relating to virtual content), possibly forpassage to the display 62 after such processing or retrieval. The localprocessing and data module 70 may be operatively coupled bycommunication links 76, 78, such as via a wired or wirelesscommunication links, to the remote processing module 72 and remote datarepository 74 such that these remote modules 72, 74 are operativelycoupled to each other and available as resources to the local processingand data module 70. In some embodiments, the local processing and datamodule 70 may include one or more of the image capture devices,microphones, inertial measurement units, accelerometers, compasses, GPSunits, radio devices, and/or gyros. In some other embodiments, one ormore of these sensors may be attached to the frame 64, or may bestandalone structures that communicate with the local processing anddata module 70 by wired or wireless communication pathways.

With continued reference to FIG. 2, in some embodiments, the remoteprocessing module 72 may comprise one or more processors configured toanalyze and process data and/or image information. In some embodiments,the remote data repository 74 may comprise a digital data storagefacility, which may be available through the internet or othernetworking configuration in a “cloud” resource configuration. In someembodiments, the remote data repository 74 may include one or moreremote servers, which provide information, e.g., information forgenerating augmented reality content, to the local processing and datamodule 70 and/or the remote processing module 72. In some embodiments,all data is stored and all computations are performed in the localprocessing and data module, allowing fully autonomous use from a remotemodule.

With reference now to FIG. 3, the perception of an image as being“three-dimensional” or “3-D” may be achieved by providing slightlydifferent presentations of the image to each eye of the viewer. FIG. 3illustrates a conventional display system for simulatingthree-dimensional imagery for a user. Two distinct images 5, 7—one foreach eye 4, 6—are outputted to the user. The images 5, 7 are spaced fromthe eyes 4, 6 by a distance 10 along an optical or z-axis parallel tothe line of sight of the viewer. The images 5, 7 are flat and the eyes4, 6 may focus on the images by assuming a single accommodated state.Such systems rely on the human visual system to combine the images 5, 7to provide a perception of depth and/or scale for the combined image.

It will be appreciated, however, that the human visual system is morecomplicated and providing a realistic perception of depth is morechallenging. For example, many viewers of conventional “3-D” displaysystems find such systems to be uncomfortable or may not perceive asense of depth at all. Without being limited by theory, it is believedthat viewers of an object may perceive the object as being“three-dimensional” due to a combination of vergence and accommodation.Vergence movements (i.e., rotation of the eyes so that the pupils movetoward or away from each other to converge the lines of sight of theeyes to fixate upon an object) of the two eyes relative to each otherare closely associated with focusing (or “accommodation”) of the lensesand pupils of the eyes. Under normal conditions, changing the focus ofthe lenses of the eyes, or accommodating the eyes, to change focus fromone object to another object at a different distance will automaticallycause a matching change in vergence to the same distance, under arelationship known as the “accommodation-vergence reflex,” as well aspupil dilation or constriction. Likewise, a change in vergence willtrigger a matching change in accommodation of lens shape and pupil size,under normal conditions. As noted herein, many stereoscopic or “3-D”display systems display a scene using slightly different presentations(and, so, slightly different images) to each eye such that athree-dimensional perspective is perceived by the human visual system.Such systems are uncomfortable for many viewers, however, since they,among other things, simply provide a different presentations of a scene,but with the eyes viewing all the image information at a singleaccommodated state, and work against the “accommodation-vergencereflex.” Display systems that provide a better match betweenaccommodation and vergence may form more realistic and comfortablesimulations of three-dimensional imagery.

FIG. 4 illustrates aspects of an approach for simulatingthree-dimensional imagery using multiple depth planes. With reference toFIG. 4, objects at various distances from eyes 4, 6 on the z-axis areaccommodated by the eyes 4, 6 so that those objects are in focus. Theeyes (4 and 6) assume particular accommodated states to bring into focusobjects at different distances along the z-axis. Consequently, aparticular accommodated state may be said to be associated with aparticular one of depth planes 14, with has an associated focaldistance, such that objects or parts of objects in a particular depthplane are in focus when the eye is in the accommodated state for thatdepth plane. In some embodiments, three-dimensional imagery may besimulated by providing different presentations of an image for each ofthe eyes 4, 6, and also by providing different presentations of theimage corresponding to each of the depth planes. While shown as beingseparate for clarity of illustration, it will be appreciated that thefields of view of the eyes 4, 6 may overlap, for example, as distancealong the z-axis increases. In addition, while shown as flat for ease ofillustration, it will be appreciated that the contours of a depth planemay be curved in physical space, such that all features in a depth planeare in focus with the eye in a particular accommodated state.

The distance between an object and the eye 4 or 6 may also change theamount of divergence of light from that object, as viewed by that eye.FIGS. 5A-5C illustrates relationships between distance and thedivergence of light rays. The distance between the object and the eye 4is represented by, in order of decreasing distance, R1, R2, and R3. Asshown in FIGS. 5A-5C, the light rays become more divergent as distanceto the object decreases. As distance increases, the light rays becomemore collimated. Stated another way, it may be said that the light fieldproduced by a point (the object or a part of the object) has a sphericalwavefront curvature, which is a function of how far away the point isfrom the eye of the user. The curvature increases with decreasingdistance between the object and the eye 4. Consequently, at differentdepth planes, the degree of divergence of light rays is also different,with the degree of divergence increasing with decreasing distancebetween depth planes and the viewer's eye 4. While only a single eye 4is illustrated for clarity of illustration in FIGS. 5A-5C and otherfigures herein, it will be appreciated that the discussions regardingeye 4 may be applied to both eyes 4 and 6 of a viewer.

Without being limited by theory, it is believed that the human eyetypically can interpret a finite number of depth planes to provide depthperception. Consequently, a highly believable simulation of perceiveddepth may be achieved by providing, to the eye, different presentationsof an image corresponding to each of these limited number of depthplanes. The different presentations may be separately focused by theviewer's eyes, thereby helping to provide the user with depth cues basedon the accommodation of the eye required to bring into focus differentimage features for the scene located on different depth plane and/orbased on observing different image features on different depth planesbeing out of focus.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user. A display system 1000 includes a stack ofwaveguides, or stacked waveguide assembly, 178 that may be utilized toprovide three-dimensional perception to the eye/brain using a pluralityof waveguides 182, 184, 186, 188, 190. In some embodiments, the displaysystem 1000 is the system 80 of FIG. 2, with FIG. 6 schematicallyshowing some parts of that system 80 in greater detail. For example, thewaveguide assembly 178 may be part of the display 62 of FIG. 2. It willbe appreciated that the display system 1000 may be considered a lightfield display in some embodiments.

With continued reference to FIG. 6, the waveguide assembly 178 may alsoinclude a plurality of features 198, 196, 194, 192 between thewaveguides. In some embodiments, the features 198, 196, 194, 192 may beone or more lenses. The waveguides 182, 184, 186, 188, 190 and/or theplurality of lenses 198, 196, 194, 192 may be configured to send imageinformation to the eye with various levels of wavefront curvature orlight ray divergence. Each waveguide level may be associated with aparticular depth plane and may be configured to output image informationcorresponding to that depth plane. Image injection devices 200, 202,204, 206, 208 may function as a source of light for the waveguides andmay be utilized to inject image information into the waveguides 182,184, 186, 188, 190, each of which may be configured, as describedherein, to distribute incoming light across each respective waveguide,for output toward the eye 4. Light exits an output surface 300, 302,304, 306, 308 of the image injection devices 200, 202, 204, 206, 208 andis injected into a corresponding input surface 382, 384, 386, 388, 390of the waveguides 182, 184, 186, 188, 190. In some embodiments, the eachof the input surfaces 382, 384, 386, 388, 390 may be an edge of acorresponding waveguide, or may be part of a major surface of thecorresponding waveguide (that is, one or both of the waveguide surfacesdirectly facing the world 144 or the viewer's eye 4). In someembodiments, a single beam of light (e.g. a collimated beam) may beinjected into each waveguide to output an entire field of clonedcollimated beams that are directed toward the eye 4 at particular angles(and amounts of divergence) corresponding to the depth plane associatedwith a particular waveguide. In some embodiments, a single one of theimage injection devices 200, 202, 204, 206, 208 may be associated withand inject light into a plurality (e.g., three) of the waveguides 182,184, 186, 188, 190.

In some embodiments, the image injection devices 200, 202, 204, 206, 208are discrete displays that each produce image information for injectioninto a corresponding waveguide 182, 184, 186, 188, 190, respectively. Insome other embodiments, the image injection devices 200, 202, 204, 206,208 are the output ends of a single multiplexed display which may, e.g.,pipe image information via one or more optical conduits (such as fiberoptic cables) to each of the image injection devices 200, 202, 204, 206,208. It will be appreciated that the image information provided by theimage injection devices 200, 202, 204, 206, 208 may include light ofdifferent wavelengths, or colors (e.g., different component colors, asdiscussed herein).

In some embodiments, the light injected into the waveguides 182, 184,186, 188, 190 is provided by a light projector system 2000, whichcomprises a light module 2040, which may include a light emitter, suchas a light emitting diode (LED). The light from the light module 2040may be directed to and modified by a light modulator 2030, e.g., aspatial light modulator, via a beam splitter 2050. The light modulator2030 may be configured to change the perceived intensity of the lightinjected into the waveguides 182, 184, 186, 188, 190. Examples ofspatial light modulators include liquid crystal displays (LCD) includinga liquid crystal on silicon (LCOS) displays.

In some embodiments, the display system 1000 may be a scanning fiberdisplay comprising one or more scanning fibers configured to projectlight in various patterns (e.g., raster scan, spiral scan, Lissajouspatterns, etc.) into one or more waveguides 182, 184, 186, 188, 190 andultimately to the eye 4 of the viewer. In some embodiments, theillustrated image injection devices 200, 202, 204, 206, 208 mayschematically represent a single scanning fiber or a bundles of scanningfibers configured to inject light into one or a plurality of thewaveguides 182, 184, 186, 188, 190. In some other embodiments, theillustrated image injection devices 200, 202, 204, 206, 208 mayschematically represent a plurality of scanning fibers or a plurality ofbundles of scanning, fibers each of which are configured to inject lightinto an associated one of the waveguides 182, 184, 186, 188, 190. Itwill be appreciated that the one or more optical fibers may beconfigured to transmit light from the light module 2040 to the one ormore waveguides 182, 184, 186, 188, 190. It will be appreciated that oneor more intervening optical structures may be provided between thescanning fiber, or fibers, and the one or more waveguides 182, 184, 186,188, 190 to, e.g., redirect light exiting the scanning fiber into theone or more waveguides 182, 184, 186, 188, 190.

A controller 210 controls the operation of one or more of the stackedwaveguide assembly 178, including operation of the image injectiondevices 200, 202, 204, 206, 208, the light source 2040, and the lightmodulator 2030. In some embodiments, the controller 210 is part of thelocal data processing module 70. The controller 210 includes programming(e.g., instructions in a non-transitory medium) that regulates thetiming and provision of image information to the waveguides 182, 184,186, 188, 190 according to, e.g., any of the various schemes disclosedherein. In some embodiments, the controller may be a single integraldevice, or a distributed system connected by wired or wirelesscommunication channels. The controller 210 may be part of the processingmodules 70 or 72 (FIG. 1) in some embodiments.

With continued reference to FIG. 6, the waveguides 182, 184, 186, 188,190 may be configured to propagate light within each respectivewaveguide by total internal reflection (TIR). The waveguides 182, 184,186, 188, 190 may each be planar or have another shape (e.g., curved),with major top and bottom surfaces and edges extending between thosemajor top and bottom surfaces. In the illustrated configuration, thewaveguides 182, 184, 186, 188, 190 may each include outcoupling opticalelements 282, 284, 286, 288, 290 that are configured to extract lightout of a waveguide by redirecting the light, propagating within eachrespective waveguide, out of the waveguide to output image informationto the eye 4. Extracted light may also be referred to as outcoupledlight and the outcoupling optical elements light may also be referred tolight extracting optical elements. An extracted beam of light isoutputted by the waveguide at locations at which the light propagatingin the waveguide strikes a light extracting optical element. Theoutcoupling optical elements 282, 284, 286, 288, 290 may, for example,be gratings, including diffractive optical features, as discussedfurther herein. While illustrated disposed at the bottom major surfacesof the waveguides 182, 184, 186, 188, 190 for ease of description anddrawing clarity, in some embodiments, the outcoupling optical elements282, 284, 286, 288, 290 may be disposed at the top and/or bottom majorsurfaces, and/or may be disposed directly in the volume of thewaveguides 182, 184, 186, 188, 190, as discussed further herein. In someembodiments, the outcoupling optical elements 282, 284, 286, 288, 290may be formed in a layer of material that is attached to a transparentsubstrate to form the waveguides 182, 184, 186, 188, 190. In some otherembodiments, the waveguides 182, 184, 186, 188, 190 may be a monolithicpiece of material and the outcoupling optical elements 282, 284, 286,288, 290 may be formed on a surface and/or in the interior of that pieceof material.

With continued reference to FIG. 6, as discussed herein, each waveguide182, 184, 186, 188, 190 is configured to output light to form an imagecorresponding to a particular depth plane. For example, the waveguide182 nearest the eye may be configured to deliver collimated light, asinjected into such waveguide 182, to the eye 4. The collimated light maybe representative of the optical infinity focal plane. The nextwaveguide up 184 may be configured to send out collimated light whichpasses through the first lens 192 (e.g., a negative lens) before it canreach the eye 4; such first lens 192 may be configured to create aslight convex wavefront curvature so that the eye/brain interprets lightcoming from that next waveguide up 184 as coming from a first focalplane closer inward toward the eye 4 from optical infinity. Similarly,the third up waveguide 186 passes its output light through both thefirst 192 and second 194 lenses before reaching the eye 4; the combinedoptical power of the first 192 and second 194 lenses may be configuredto create another incremental amount of wavefront curvature so that theeye/brain interprets light coming from the third waveguide 186 as comingfrom a second focal plane that is even closer inward toward the personfrom optical infinity than was light from the next waveguide up 184.

The other waveguide layers 188, 190 and lenses 196, 198 are similarlyconfigured, with the highest waveguide 190 in the stack sending itsoutput through all of the lenses between it and the eye for an aggregatefocal power representative of the closest focal plane to the person. Tocompensate for the stack of lenses 198, 196, 194, 192 whenviewing/interpreting light coming from the world 144 on the other sideof the stacked waveguide assembly 178, a compensating lens layer 180 maybe disposed at the top of the stack to compensate for the aggregatepower of the lens stack 198, 196, 194, 192 below. Such a configurationprovides as many perceived focal planes as there are availablewaveguide/lens pairings. Both the outcoupling optical elements of thewaveguides and the focusing aspects of the lenses may be static (i.e.,not dynamic or electro-active). In some alternative embodiments, eitheror both may be dynamic using electro-active features.

In some embodiments, two or more of the waveguides 182, 184, 186, 188,190 may have the same associated depth plane. For example, multiplewaveguides 182, 184, 186, 188, 190 may be configured to output imagesset to the same depth plane, or multiple subsets of the waveguides 182,184, 186, 188, 190 may be configured to output images set to the sameplurality of depth planes, with one set for each depth plane. This canprovide advantages for forming a tiled image to provide an expandedfield of view at those depth planes.

With continued reference to FIG. 6, the outcoupling optical elements282, 284, 286, 288, 290 may be configured to both redirect light out oftheir respective waveguides and to output this light with theappropriate amount of divergence or collimation for a particular depthplane associated with the waveguide. As a result, waveguides havingdifferent associated depth planes may have different configurations ofoutcoupling optical elements 282, 284, 286, 288, 290, which output lightwith a different amount of divergence depending on the associated depthplane. In some embodiments, the light extracting optical elements 282,284, 286, 288, 290 may be volumetric or surface features, which may beconfigured to output light at specific angles. For example, the lightextracting optical elements 282, 284, 286, 288, 290 may be volumeholograms, surface holograms, and/or diffraction gratings. In someembodiments, the features 198, 196, 194, 192 may not be lenses; rather,they may simply be spacers (e.g., cladding layers and/or structures forforming air gaps).

In some embodiments, the outcoupling optical elements 282, 284, 286,288, 290 are diffractive features that form a diffraction pattern, or“diffractive optical element” (also referred to herein as a “DOE”).Preferably, the DOE's have a sufficiently low diffraction efficiency sothat only a portion of the light of the beam is deflected away towardthe eye 4 with each intersection of the DOE, while the rest continues tomove through a waveguide via total internal reflection. The lightcarrying the image information is thus divided into a number of relatedexit beams that exit the waveguide at a multiplicity of locations andthe result is a fairly uniform pattern of exit emission toward the eye 4for this particular collimated beam bouncing around within a waveguide.

In some embodiments, one or more DOEs may be switchable between “on”states in which they actively diffract, and “off” states in which theydo not significantly diffract. For instance, a switchable DOE maycomprise a layer of polymer dispersed liquid crystal, in whichmicrodroplets comprise a diffraction pattern in a host medium, and therefractive index of the microdroplets may be switched to substantiallymatch the refractive index of the host material (in which case thepattern does not appreciably diffract incident light) or themicrodroplet may be switched to an index that does not match that of thehost medium (in which case the pattern actively diffracts incidentlight).

In some embodiments, a camera assembly 500 (e.g., a digital camera,including visible light and infrared light cameras) may be provided tocapture images of the eye 4 and/or tissue around the eye 4 to, e.g.,detect user inputs. As used herein, a camera may be any image capturedevice. In some embodiments, the camera assembly 500 may include animage capture device and a light source to project light (e.g., infraredlight) to the eye, which may then be reflected by the eye and detectedby the image capture device. In some embodiments, the camera assembly500 may be attached to the frame 64 (FIG. 2) and may be in electricalcommunication with the processing modules 70 and/or 72, which mayprocess image information from the camera assembly 500. In someembodiments, one camera assembly 500 may be utilized for each eye, toseparately monitor each eye.

With reference now to FIG. 7, an example of exit beams outputted by awaveguide is shown. One waveguide is illustrated, but it will beappreciated that other waveguides in the waveguide assembly 178 (FIG. 6)may function similarly, where the waveguide assembly 178 includesmultiple waveguides. Light 400 is injected into the waveguide 182 at theinput surface 382 of the waveguide 182 and propagates within thewaveguide 182 by TIR. At points where the light 400 impinges on the DOE282, a portion of the light exits the waveguide as exit beams 402. Theexit beams 402 are illustrated as substantially parallel but, asdiscussed herein, they may also be redirected to propagate to the eye 4at an angle (e.g., forming divergent exit beams), depending on the depthplane associated with the waveguide 182. It will be appreciated thatsubstantially parallel exit beams may be indicative of a waveguide withoutcoupling optical elements that outcouple light to form images thatappear to be set on a depth plane at a large distance (e.g., opticalinfinity) from the eye 4. Other waveguides or other sets of outcouplingoptical elements may output an exit beam pattern that is more divergent,which would require the eye 4 to accommodate to a closer distance tobring it into focus on the retina and would be interpreted by the brainas light from a distance closer to the eye 4 than optical infinity.

In some embodiments, a full color image may be formed at each depthplane by overlaying images in each of the component colors, e.g., threeor more component colors. FIG. 8 illustrates an example of a stackedwaveguide assembly in which each depth plane includes images formedusing multiple different component colors. The illustrated embodimentshows depth planes 14 a-14 f, although more or fewer depths are alsocontemplated. Each depth plane may have three component color imagesassociated with it: a first image of a first color, G; a second image ofa second color, R; and a third image of a third color, B. Differentdepth planes are indicated in the figure by different numbers fordiopters (dpt) following the letters G, R, and B. Just as examples, thenumbers following each of these letters indicate diopters (1/m), orinverse distance of the depth plane from a viewer, and each box in thefigures represents an individual component color image. In someembodiments, to account for differences in the eye's focusing of lightof different wavelengths, the exact placement of the depth planes fordifferent component colors may vary. For example, different componentcolor images for a given depth plane may be placed on depth planescorresponding to different distances from the user. Such an arrangementmay increase visual acuity and user comfort.

In some embodiments, light of each component color may be outputted by asingle dedicated waveguide and, consequently, each depth plane may havemultiple waveguides associated with it. In such embodiments, each box inthe figures including the letters G, R, or B may be understood torepresent an individual waveguide, and three waveguides may be providedper depth plane where three component color images are provided perdepth plane. While the waveguides associated with each depth plane areshown adjacent to one another in this drawing for ease of description,it will be appreciated that, in a physical device, the waveguides mayall be arranged in a stack with one waveguide per level. In some otherembodiments, multiple component colors may be outputted by the samewaveguide, such that, e.g., only a single waveguide may be provided perdepth plane.

With continued reference to FIG. 8, in some embodiments, G is the colorgreen, R is the color red, and B is the color blue. In some otherembodiments, other colors associated with other wavelengths of light,including magenta and cyan, may be used in addition to or may replaceone or more of red, green, or blue.

It will be appreciated that references to a given color of lightthroughout this disclosure will be understood to encompass light of oneor more wavelengths within a range of wavelengths of light that areperceived by a viewer as being of that given color. For example, redlight may include light of one or more wavelengths in the range of about620-780 nm, green light may include light of one or more wavelengths inthe range of about 492-577 nm, and blue light may include light of oneor more wavelengths in the range of about 435-493 nm.

With reference now to FIG. 9A, in some embodiments, light impinging on awaveguide may need to be redirected to incouple that light into thewaveguide. An incoupling optical element may be used to redirect andincouple the light into its corresponding waveguide. FIG. 9A illustratesa cross-sectional side view of an example of a plurality or set 1200 ofstacked waveguides that each includes an incoupling optical element. Thewaveguides may each be configured to output light of one or moredifferent wavelengths, or one or more different ranges of wavelengths.It will be appreciated that the stack 1200 may correspond to the stack178 (FIG. 6) and the illustrated waveguides of the stack 1200 maycorrespond to part of the plurality of waveguides 182, 184, 186, 188,190, except that light from one or more of the image injection devices200, 202, 204, 206, 208 is injected into the waveguides from a positionthat requires light to be redirected for incoupling.

The illustrated set 1200 of stacked waveguides includes waveguides 1210,1220, and 1230. Each waveguide includes an associated incoupling opticalelement (which may also be referred to as a light input area on thewaveguide), with, e.g., incoupling optical element 1212 disposed on amajor surface (e.g., an upper major surface) of waveguide 1210,incoupling optical element 1222 disposed on a major surface (e.g., anupper major surface) of waveguide 1220, and incoupling optical element1232 disposed on a major surface (e.g., an upper major surface) ofwaveguide 1230. In some embodiments, one or more of the incouplingoptical elements 1212, 1222, 1232 may be disposed on the bottom majorsurface of the respective waveguide 1210, 1220, 1230 (particularly wherethe one or more incoupling optical elements are reflective, deflectingoptical elements). As illustrated, the incoupling optical elements 1212,1222, 1232 may be disposed on the upper major surface of theirrespective waveguide 1210, 1220, 1230 (or the top of the next lowerwaveguide), particularly where those incoupling optical elements aretransmissive, deflecting optical elements. In some embodiments, theincoupling optical elements 1212, 1222, 1232 may be disposed in the bodyof the respective waveguide 1210, 1220, 1230. In some embodiments, asdiscussed herein, the incoupling optical elements 1212, 1222, 1232 arewavelength selective, such that they selectively redirect one or morewavelengths of light, while transmitting other wavelengths of light.While illustrated on one side or corner of their respective waveguide1210, 1220, 1230, it will be appreciated that the incoupling opticalelements 1212, 1222, 1232 may be disposed in other areas of theirrespective waveguide 1210, 1220, 1230 in some embodiments.

As illustrated, the incoupling optical elements 1212, 1222, 1232 may belaterally offset from one another. In some embodiments, each incouplingoptical element may be offset such that it receives light without thatlight passing through another incoupling optical element. For example,each incoupling optical element 1212, 1222, 1232 may be configured toreceive light from a different image injection device 1213, 1223, 1233and may be separated (e.g., laterally spaced apart) from otherincoupling optical elements 1212, 1222, 1232 such that it substantiallydoes not receive light from the other ones of the incoupling opticalelements 1212, 1222, 1232.

Each waveguide also includes associated light distributing elements,with, e.g., light distributing elements 1214 disposed on a major surface(e.g., a top major surface) of waveguide 1210, light distributingelements 1224 disposed on a major surface (e.g., a top major surface) ofwaveguide 1220, and light distributing elements 1234 disposed on a majorsurface (e.g., a top major surface) of waveguide 1230. In some otherembodiments, the light distributing elements 1214, 1224, 1234, may bedisposed on a bottom major surface of associated waveguides 1210, 1220,1230, respectively. In some other embodiments, the light distributingelements 1214, 1224, 1234, may be disposed on both top and bottom majorsurface of associated waveguides 1210, 1220, 1230, respectively; or thelight distributing elements 1214, 1224, 1234, may be disposed ondifferent ones of the top and bottom major surfaces in differentassociated waveguides 1210, 1220, 1230, respectively.

The waveguides 1210, 1220, 1230 may be spaced apart and separated by,e.g., gas, liquid, and/or solid layers of material. For example, asillustrated, layer 1218 a may separate waveguides 1210 and 1220; andlayer 1218 b may separate waveguides 1220 and 1230. In some embodiments,the layers 1218 a and 1218 b are formed of low refractive indexmaterials (that is, materials having a lower refractive index than thematerial forming the immediately adjacent one of waveguides 1210, 1220,1230). Preferably, the refractive index of the material forming thelayers 1218 a, 1218 b is 0.05 or more, or 0.10 or more less than therefractive index of the material forming the waveguides 1210, 1220,1230. Advantageously, the lower refractive index layers 1218 a, 1218 bmay function as cladding layers that facilitate total internalreflection (TIR) of light through the waveguides 1210, 1220, 1230 (e.g.,TIR between the top and bottom major surfaces of each waveguide). Insome embodiments, the layers 1218 a, 1218 b are formed of air. While notillustrated, it will be appreciated that the top and bottom of theillustrated set 1200 of waveguides may include immediately neighboringcladding layers.

Preferably, for ease of manufacturing and other considerations, thematerial forming the waveguides 1210, 1220, 1230 are similar or thesame, and the material forming the layers 1218 a, 1218 b are similar orthe same. In some embodiments, the material forming the waveguides 1210,1220, 1230 may be different between one or more waveguides, and/or thematerial forming the layers 1218 a, 1218 b may be different, while stillholding to the various refractive index relationships noted above.

With continued reference to FIG. 9A, light rays 1240, 1242, 1244 areincident on the set 1200 of waveguides. It will be appreciated that thelight rays 1240, 1242, 1244 may be injected into the waveguides 1210,1220, 1230 by one or more image injection devices 200, 202, 204, 206,208 (FIG. 6).

In some embodiments, the light rays 1240, 1242, 1244 have differentproperties, e.g., different wavelengths or different ranges ofwavelengths, which may correspond to different colors. The incouplingoptical elements 1212, 122, 1232 each deflect the incident light suchthat the light propagates through a respective one of the waveguides1210, 1220, 1230 by TIR. In some embodiments, the incoupling opticalelements 1212, 122, 1232 each selectively deflect one or more particularwavelengths of light, while transmitting other wavelengths to anunderlying waveguide and associated incoupling optical element.

For example, incoupling optical element 1212 may be configured todeflect ray 1240, which has a first wavelength or range of wavelengths,while transmitting rays 1242 and 1244, which have different second andthird wavelengths or ranges of wavelengths, respectively. Thetransmitted ray 1242 then impinges on and is deflected by the incouplingoptical element 1222, which is configured to selectively deflect lightof second wavelength or range of wavelengths. The ray 1244 istransmitted by the incoupling optical element 1222 and continues on toimpinge on and be deflected by the incoupling optical element 1232,which is configured to selectively deflect light of third wavelength orrange of wavelengths.

With continued reference to FIG. 9A, the deflected light rays 1240,1242, 1244 are deflected so that they propagate through a correspondingwaveguide 1210, 1220, 1230; that is, the incoupling optical elements1212, 1222, 1232 of each waveguide deflects light into thatcorresponding waveguide 1210, 1220, 1230 to incouple light into thatcorresponding waveguide. The light rays 1240, 1242, 1244 are deflectedat angles that cause the light to propagate through the respectivewaveguide 1210, 1220, 1230 by TIR. The light rays 1240, 1242, 1244propagate through the respective waveguide 1210, 1220, 1230 by TIR untilimpinging on the waveguide's corresponding light distributing elements1214, 1224, 1234.

With reference now to FIG. 9B, a perspective view of an example of theplurality of stacked waveguides of FIG. 9A is illustrated. As notedabove, the incoupled light rays 1240, 1242, 1244, are deflected by theincoupling optical elements 1212, 1222, 1232, respectively, and thenpropagate by TIR within the waveguides 1210, 1220, 1230, respectively.The light rays 1240, 1242, 1244 then impinge on the light distributingelements 1214, 1224, 1234, respectively. The light distributing elements1214, 1224, 1234 deflect the light rays 1240, 1242, 1244 so that theypropagate towards the outcoupling optical elements 1250, 1252, 1254,respectively.

In some embodiments, the light distributing elements 1214, 1224, 1234are orthogonal pupil expanders (OPE's). In some embodiments, the OPE'sboth deflect or distribute light to the outcoupling optical elements1250, 1252, 1254 and also increase the beam or spot size of this lightas it propagates to the outcoupling optical elements. In someembodiments, e.g., where the beam size is already of a desired size, thelight distributing elements 1214, 1224, 1234 may be omitted and theincoupling optical elements 1212, 1222, 1232 may be configured todeflect light directly to the outcoupling optical elements 1250, 1252,1254. For example, with reference to FIG. 9A, the light distributingelements 1214, 1224, 1234 may be replaced with outcoupling opticalelements 1250, 1252, 1254, respectively. In some embodiments, theoutcoupling optical elements 1250, 1252, 1254 are exit pupils (EP's) orexit pupil expanders (EPE's) that direct light in a viewer's eye 4 (FIG.7).

Accordingly, with reference to FIGS. 9A and 9B, in some embodiments, theset 1200 of waveguides includes waveguides 1210, 1220, 1230; incouplingoptical elements 1212, 1222, 1232; light distributing elements (e.g.,OPE's) 1214, 1224, 1234; and outcoupling optical elements (e.g., EP's)1250, 1252, 1254 for each component color. The waveguides 1210, 1220,1230 may be stacked with an air gap/cladding layer between each one. Theincoupling optical elements 1212, 1222, 1232 redirect or deflectincident light (with different incoupling optical elements receivinglight of different wavelengths) into its waveguide. The light thenpropagates at an angle which will result in TIR within the respectivewaveguide 1210, 1220, 1230. In the example shown, light ray 1240 (e.g.,blue light) is deflected by the first incoupling optical element 1212,and then continues to bounce down the waveguide, interacting with thelight distributing element (e.g., OPE's) 1214 and then the outcouplingoptical element (e.g., EPs) 1250, in a manner described earlier. Thelight rays 1242 and 1244 (e.g., green and red light, respectively) willpass through the waveguide 1210, with light ray 1242 impinging on andbeing deflected by incoupling optical element 1222. The light ray 1242then bounces down the waveguide 1220 via TIR, proceeding on to its lightdistributing element (e.g., OPEs) 1224 and then the outcoupling opticalelement (e.g., EP's) 1252. Finally, light ray 1244 (e.g., red light)passes through the waveguide 1220 to impinge on the light incouplingoptical elements 1232 of the waveguide 1230. The light incouplingoptical elements 1232 deflect the light ray 1244 such that the light raypropagates to light distributing element (e.g., OPEs) 1234 by TIR, andthen to the outcoupling optical element (e.g., EPs) 1254 by TIR. Theoutcoupling optical element 1254 then finally outcouples the light ray1244 to the viewer, who also receives the outcoupled light from theother waveguides 1210, 1220.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B. As illustrated, the waveguides1210, 1220, 1230, along with each waveguide's associated lightdistributing element 1214, 1224, 1234 and associated outcoupling opticalelement 1250, 1252, 1254, may be vertically aligned. However, asdiscussed herein, the incoupling optical elements 1212, 1222, 1232 arenot vertically aligned; rather, the incoupling optical elements arepreferably non-overlapping (e.g., laterally spaced apart as seen in thetop-down view). As discussed further herein, this nonoverlapping spatialarrangement facilitates the injection of light from different resourcesinto different waveguides on a one-to-one basis, thereby allowing aspecific light source to be uniquely coupled to a specific waveguide. Insome embodiments, arrangements including nonoverlappingspatially-separated incoupling optical elements may be referred to as ashifted pupil system, and the incoupling optical elements within thesearrangements may correspond to sub pupils.

Example Etches for High Refractive Index Glasses

In some embodiments, microscale and nanoscale features, such the variousdiffractive optical elements discussed herein, may be etched directly ina high refractive index glass substrate. For example, the glasssubstrate may be used as a waveguide and the plasma etching processesmay be used to form the incoupling optical elements 1212, 1222, 1232,the light distributing elements 1214, 1224, 1234, and/or the outcouplingoptical element 1250, 1252, 1254 of FIGS. 9A-9C directly in thesubstrate.

The high refractive index glass forming the substrates may have arelatively low concentration of silicon dioxide (SiO₂), e.g., less than50 weight percent (wt %) SiO₂. In addition, these high refractive indexglasses may comprise 50 wt % or more of one or more metal oxides, suchas B₂O₃, Al₂O₃, ZrO₂, Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, ZnO, La₂O₃,Nb₂O₅, TiO₂, HfO, and Sb₂O₃. In some embodiments, the glasses mayinclude combinations of these metal oxides.

While providing a high refractive index, the low amounts of SiO₂ andhigh amounts of other metal oxides may prevent effective etching ofsubstrates formed using these glasses. For example, glasses formed bysuch combinations of component oxides may be particularly difficult toetch. Even where specific etching recipes have been developed for acomponent oxide, these etching recipes may not be effective for highrefractive index glasses due to the relatively low concentration of SiO₂and differing etch rates between the constituent component oxidesforming a glass.

In addition, conventional etches processes exhibit various deficiencies.For example, wet chemical etching is typically limited to a patterningresolution on the order of microns and is isotropic, which may not formstraight sidewalls. Alternatively, ion milling may be used tounselectively remove material from high refractive index glasssubstrates; however, this process severely limits the attainableresolution and aspect ratios of patterned features. Ion milling mayremove material simply by bombarding a surface with high-energyparticles that physically sputter away material from that surface. Ionmilling requires a hardmask, but also erodes the hardmask, such that theprocess may be unable to maintain the mask for a sufficient duration toform high aspect ratio features.

According to some embodiments, as discussed herein, a plasma etchingprocess has been developed to form features in a high refractive indexglass substrate. The features may be formed by using the plasma etchingprocess to transfer a pattern from a mask layer to the high refractiveindex glass substrate underlying the mask layer. The plasma etchingprocess may be anisotropic, or directional, and may be highly selectivefor the glass substrate relative to the mask layer. The featuresproduced as a result of the plasma etching process may havesubstantially vertical sidewalls. In some embodiments, the plasmaetching process may not be selective for all oxides that may form thehigh refractive index glass substrate. In some embodiments, the plasmaetching process may include both chemical and physical mechanisms foretching the high refractive index glass, with the physical mechanismsallowing the removal of oxide species for which the chemical mechanismsmay not be highly effective in removing. Without being limited bytheory, chemical etching of at least some substrate material may disruptthe physical integrity of the exposed substrate, thereby allowing thephysical mechanisms to remove exposed material with higher selectivitythan would occur without the chemical etching. Thus, a high resolutionpattern may be transferred to the high refractive index glass substratevia the plasma etching process, even where the high refractive indexglass comprises a complex mixture of oxides.

In some embodiments, the substrate may be patterned by selectivelyexposing some areas of the surface of the substrate to reactive species.That is, some areas of the substrate may be etched while other areas maynot be etched in order to form features therein. For example, apatterned masking material or mask layer which resists etching mayoverlay the substrate such that the area under the mask layer is notetched while the area unprotected or left exposed by the mask layer isetched. The mask layer may then be removed to leave the etched featureson the surface of the substrate.

As discussed herein, the plasma etching process may be an anisotropic,or substantially anisotropic, etching process. The directionality of theanisotropic etch advantageously allows the formation of substantiallystraight sidewalls. Where etchant species are directed towards thesubstrate in a direction perpendicular to the substrate, the etchingprocess may define features in the substrate with substantially verticalsidewalls. In some embodiments, straight, angled (non-vertical)sidewalls may be formed by directing etchant species to the substrate atan angle that is not perpendicular to the substrate.

In some embodiments, the plasma etching process may etch two or moreoxides, which comprise a high refractive index glass, at substantiallysimilar rates. In some embodiments, the etch rate may be substantiallysimilar for any two or more of SiO₂, B₂O₃, Al₂O₃, ZrO₂, Li₂O, Na₂O, K₂O,MgO, CaO, SrO, BaO, ZnO, La₂O₃, Nb₂O₅, TiO₂, HfO, and Sb₂O₃.

It will be appreciated that the term “high refractive index” is usedherein to refer to materials, preferably optically transmissivematerials such as glasses, that have a refractive index greater than orequal to 1.65. In some embodiments, a high refractive index glass mayhave a refractive index of 1.65 or greater, 1.7 or greater, 1.75 orgreater, or 1.8 or greater. In some embodiments, the refractive indexmay be as noted above and also less than 4, less than 3, or less than2.5. In some other embodiments, the etching processes described hereinmay be applied to etch substrates having a refractive index lower than1.65.

In some embodiments, the high refractive index glass comprises less thanabout 50 percent by weight (wt %) SiO₂. In some embodiments, the highrefractive index glass may comprises less than about 30 wt % SiO₂, lessthan about 25 wt % SiO₂, or less than about 20 wt % SiO₂. In someembodiments, the remainder of the high refractive index glass maycomprise at least one metal oxide, including a plurality of metaloxides; that is, a high refractive index glass may comprise greater thanabout 50 wt % of one or a plurality of metal oxides such as B₂O₃, Al₂O₃,ZrO₂, Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, ZnO, La₂O₃, Nb₂O₅, TiO₂, HfO,and Sb₂O₃. The high refractive index glass may comprise up to about 30wt % of any one metal oxide in some embodiments.

According to certain embodiments, the high refractive index glass maycomprise SiO₂, B₂O₃, TiO₂, La₂O₃, ZrO₂, Nb₂O₅, CaO, and Li₂O. Forexample, the high refractive index glass may comprise between about 20wt % to about 30 wt % SiO₂, between about 0 wt % and 5 wt % B₂O₃,between about 5 wt % and 10 wt % TiO₂, between about 20 wt % and 25 wt %La₂O₃, between about 5 wt % and 10 wt % ZrO₂, between about 10 wt % and15 wt % Nb₂O₅, between about 15 wt % and 20 wt % CaO, and between about0 wt % and 5 wt % Li₂O.

According to some embodiments, the plasma etching process described maybe used to form features having a critical dimension within a range fromabout 10 nm to about 10 μm. As used herein, the critical dimensionrefers to the minimum dimension of features formed in a substrate, asseen in a top-down view. For example, the critical dimension of agrating formed by identical elongated features is the width of one ofthe features, as seen in the top-down view. In some embodiments, thecritical dimension of a feature formed in a high refractive index glasssubstrate may be within a range from about 10 nm to about 500 nm,including about 10 nm to about 100 nm, or about 100 nm to about 500 nm.In some embodiments, the features formed by the plasma etching processcomprise substantially vertical sidewalls. In some embodiments, an angleformed between a feature formed by the plasma etching process, such as asidewall, and a horizontal surface of the substrate may be greater than75°, greater than 80°, or greater than 85°.

In some embodiments, the plasma etching process may form features thathave an aspect ratio in a range from about 1:10 to about 10:1, fromabout 1:10 to about 3:1, or from about 3:1 to about 10:1. It will beappreciated that the aspect ratio is the ratio of the width of a featureand the height of the feature.

Reference will now be made to FIG. 10, which shows a process flowdiagram for an example of a plasma etching process according to someembodiments. A substrate comprising a high refractive index glass asdescribed herein is provided at block 1001. A mask layer comprising apattern of openings is provided on the high refractive index glasssubstrate at block 1002, such that at least a portion of the highrefractive index glass substrate is exposed by the mask layer. In someembodiments, the mask layer may comprise, for example, a polymericphotoresist layer or hardmask having a desired pattern, such as a binarygrating pattern. In some embodiments, blocks 1001 and 1002 may becombined. For example, the etch process may start with a high refractiveindex glass substrate in an etch chamber, with the substrate having anoverlying patterned mask layer.

The high refractive index glass substrate and mask layer are exposed toa plasma in a reaction chamber at block 1003 until a desired amount ofhigh refractive index glass has been removed from the portion orportions of the high refractive index glass substrate that are exposedby openings in the mask layer to thereby form the desired pattern in thehigh refractive index glass substrate. Preferably, as discussed herein,plasma comprises chemical and physical etching species. Any mask layerremaining over the high refractive index glass substrate may be removedat block 1004. Such a removal may be accomplished, for example, bycontacting the remaining mask layer with a solvent that dissolves thelayer or using an ashing process.

In some embodiments, the mask layer may be patterned at block 1002 by alithographic technique. For example, the mask layer may be patterned byultraviolet photolithography, nanoimprinting, e-beam lithography, orother techniques for removing material at selected areas of the masklayer to form openings that expose the underlying glass substrate.

In some embodiments, the mask layer may comprise a polymer, for examplea polymeric resist material, e.g., a photoresist material. In someembodiments, the mask layer may be a hardmask layer. In someembodiments, the hardmask layer may comprise a metal such as nickel, oramorphous carbon.

In some embodiments, the mask layer may provide an etch selectivityratio in a range of about 0.1 to about 10. As used herein, the etchselectivity ratio refers to the ratio of the etch rate of a highrefractive index glass substrate relative to the etch rate of the masklayer. In some embodiments, the mask layer may have an etch selectivityratio of greater than about 0.5, greater than about 1, greater thanabout 2, or greater than about 5, up to about 10. The thickness of themask layer may be selected based upon the depth of features to be formedby the subsequent exposure to etchant species. For example, thethickness may be selected to be sufficiently thick, in view of theselectivity provided by the etchant species and the etch conditions,such that the mask layer is not worn away by the subsequent exposure tothe etchant species. In some embodiments, the critical dimensions orwidths of features in the mask layer also may be sufficiently largerthan the desired sizes of substrate features to be patterned using thesemass features, to compensate for reductions in width caused by etchingwith the etchant species. In some embodiments, features in the masklayer may be formed to a sufficiently large size by first patterning themask layer and then augmenting the sizes of the features by conformallydepositing (e.g., by CVD or ALD) an additional layer of mask materialover those features. The additional conformal layer of mask material maybe formed of the same or a different material than the underlyingpatterned mask layer.

In some embodiments the patterned mask layer may be on a high refractiveindex glass substrate. The mask layer may comprise a plurality ofsubstantially parallel lines formed on the surface of the highrefractive index glass. In some embodiments, the lines may havethicknesses of about 100 nm and base widths of about 135 nm. It will beappreciated that the mask layer may be patterned to have shapes otherthan lines. For example, in some embodiments, the mask layer pattern maycomprise any pattern, shape, or design, and may have a criticaldimension of about 10-500 nm.

In some embodiments, the mask layer pattern may comprise a patterncorresponding to an optical element, such as a diffraction grating orDOE. In some embodiments, the mask layer pattern may comprise a binarydiffraction grating. As discussed herein, in some embodiments, the masklayer pattern may comprise an incoupling optical element, an outcouplingoptical element, or a light distributing element, for example as shownin FIGS. 9A-9C.

The high refractive index glass substrate having the overlying masklayer may be provided in a plasma etch chamber of a plasma reactor andthen exposed to a plasma at block 1003. Providing the substrate in thereaction chamber may include loading the substrate into the reactionchamber. In some embodiments, a plasma may be generated in the reactionchamber, that is, in situ. In some embodiments a plasma may be generatedin a second, different chamber upstream of the reaction chamber, such asa remote plasma generator, and provided to the reaction chamberaccommodating the high refractive index glass substrate. In someembodiments, the plasma reactor may be an inductively coupled plasma(ICP) reactor. In some embodiments, the plasma reactor may be a dualfrequency ICP reactor.

A plasma to which the high refractive index glass substrate and masklayer is exposed at block 1003 may be a plasma generated with a sourcegas in the plasma reactor. Thus, in some embodiments the plasma maycomprise ions, radicals, atoms, and/or other high energy reactivespecies formed from the source gas. In some embodiments, the sourcegases may be flowed continuously into the plasma etch chamber during theplasma exposure block 1003.

The source gas may comprise one or a plurality of gases. In someembodiments, the source gas may comprise an inert gas, such as He, Ne,Ar, Kr, or Xe, and one or more of the following for forming a chemicallyreactive species: O₂, N₂, H₂, and halide gases, such as XeF₂, C₂F₆, CF₄,CHF₃, CF₃Cl, SF₆, Cl₂, BCL, and HBr. In some embodiments, the source gasmay be flowed into the plasma etch chamber and may contact the highrefractive index glass substrate before a plasma is ignited or generatedin the plasma etch chamber.

As examples, the source gas may comprise SF₆ and Ar. In some otherexamples, the source gas may comprise CHF₃ and Ar. In yet otherexamples, the source gas may comprise CHF₃, CF₄, and Ar. Other examplesof source gas compositions may comprise BCl₃ and HBr. In other examples,the source gas may comprise BCl₃, HBr, and Ar. In some embodiments, thesource gas may comprise Ar and at least one other halide gas.

In some embodiments, exposing the substrate to a plasma may compriseexposing the substrate to a plasma-excited species generated from anoble gas, such as He, Ne, Ar, Kr, or Xe. For example, theplasma-excited species may be in the form of radicals, ions, plasma, ormay be in elemental form. In some embodiments, the plasma may compriseSF₆ radicals, SF₆ molecules, and/or SF₆ plasma. In some embodiments, theplasma may comprise HBr radicals, HBr molecules, and/or HBr plasma. Insome embodiments, the plasma may comprise BCl₃ radicals, BCl₃ molecules,and/or BCl₃ plasma. In some embodiments, the plasma may comprise CHF₃radicals, CHF₃ molecules, and/or CHF₃ plasma. In some other embodiments,the plasma may comprise CF₄ radicals, CF₄ molecules, and/or CF₄ plasma.

In some embodiments, the total flow rate for the source gas into theplasma etch chamber may be in the range from less than about 1 sccm toabout 100 sccm, or from about 25 sccm to about 75 sccm. In someembodiments, a flow rate for any one component gas of the source gas maybe in the range from about 1 sccm to about 100 sccm. As an example,where the source gas comprises SF₆ and Ar, a flow rate for SF₆ may inthe range from about 1 sccm to 100 about 100 sccm, preferably about 50sccm, and a flow rate for Ar may be in the range from about 1 sccm toabout 100 sccm, preferably about 50 sccm.

The surface of the high refractive index glass substrate and mask layerare exposed to a plasma in a reaction chamber at block 1003 until adesired amount of high refractive index glass has been removed from theportion or portions of the high refractive index glass substrate thatare left exposed by the patterned mask layer. The removal of materialtransfers the pattern or structure form the mask layer into the highrefractive index glass substrate. The duration for which the highrefractive index glass substrate and mask layer are exposed to theplasma at block 1003 may be readily determined by the skilled artisandepending on the desired amount of material to be removed from the highrefractive index glass substrate. For example, the high refractive indexglass substrate and mask layer may be exposed to a plasma for a durationin the range of from less than 1 second to about 1 minute, or from about5 seconds to about 30 seconds. In some embodiments, plasma exposuretimes of greater than about 1 minute may be used depending on thedesired amount of high refractive index glass material to be removed andthe thickness and composition of the mask layer.

In some embodiments, mask layer material may be removed by the plasma.Therefore, in some embodiments, the plasma exposure duration may belimited by the thickness of the mask layer and/or mask layer material.For example, the plasma exposure duration may be sufficiently short thatholes extending the thickness of the mask layer are not formed.

Without wishing to be bound by theory, as discussed herein, a plasmaaccording to some embodiments may remove material from the highrefractive index glass substrate by both a physical etching mechanismand a chemical etching mechanism. In some embodiments, the source gasmay comprise a gas which may etch a substrate by a physical mechanismwhen a plasma is generated therein, such as Ar, He, or N₂, and a gaswhich may etch a substrate by a chemical mechanism when a plasm isgenerated therein, such as CF₄, CHF₃, SF₆, O₂, Cl₂, BCl₃, HBr, and/orother halide gases.

The plasma may be generated by applying RF power to the source gas. TheRF power may be applied to the source gas that flows during the plasmaexposure block 1003, and/or that flows through a remote plasmagenerator. In some embodiments, the RF power applied to the source gasis in the range from about 10 W to about 500 W, from about 100 W toabout 200 W, from about 200 W to about 500 W, or from about 10 W toabout 100 W.

In some embodiments, where a plasma is generated in an ICP reactor, afirst ICP power may be applied to the source gas to generate a plasmaand a second RF power may be applied to the source gas and/or plasma inthe reaction chamber to generate a directional electric field thereinto, e.g., facilitate anisotropic etching by directing etchant species tothe substrate in a straight line. In some embodiments, the ICP power maybe in a range from about 10 W to about 2500 W. In some embodiments, theRF power may be in a range from about 10 W to about 500 W, from about100 W to about 200 W, from about 200 W to about 500 W, or from about 10W to about 100 W.

In some embodiments, for example where a dual frequency ICP reaction isused to generate a plasma, a first VHF power is applied to the sourcegas and a second RF power is applied to the source gas and/or plasma inthe reaction chamber to generate a directional electric field therein.In some embodiments, the VHF power applied to the source gas may be in arange from about 10 W to about 2500 W. In some embodiments, the RF powermay be in a range from about 10 W to about 500 W, from about 100 W toabout 200 W, from about 200 W to about 500 W, or from about 10 W toabout 100 W.

According to some embodiments a plasma may be generated with the plasmaetch chamber having a pressure of from about 1 Torr to about 0.1 mTorr.More particularly, the reaction chamber pressure may be in a range fromabout 5 mTorr to about 20 mTorr, or from about 20 mTorr to about 100mTorr in some embodiments. Without being bound by theory, it is believedthat a relatively low reaction chamber pressure as compared with othertypical plasma etching processes may reduce the tendency of any chemicaletching mechanism to isotropically etch portions of the substrate. Insome embodiments, a relatively low pressure, from example, a reactionchamber pressure from about 20 mTorr to about 100 mTorr may facilitatethe formation of features having substantially vertical sidewalls.

In some embodiments, a plasma may be generated at a temperature of in arange from about −150° C. to about 50° C. In some embodiments, a plasmamay be generated at a temperature in a range from about −120° C. toabout −100° C., from about −100° C. to about 0° C., from about 0° C. toabout 20° C., and from about 20° C. to about 50° C.

With reference now to FIGS. 11A-11C, in some embodiments, an etch maskmay be biased to facilitate the formation of features of desired sizesin a high refractive index glass substrate. Advantageously, the etchmask may be utilized in the patterning of underlying glass substratesusing conventional directional etches, e.g., ion beam milling, and/orthe plasma etching processes disclosed herein.

FIG. 11A illustrates a cross-sectional side view of an example of aglass substrate 1010 having an overlying etch mask 1012. The glasssubstrate 1010 may be formed of any of the high refractive index glassmaterials disclosed herein. For example, the material forming the glasssubstrate may have a refractive index of about 1.65 or more or 1.75 ormore, and less than about 50 wt % SiO₂. In some embodiments, more than50 wt % of the substrate is formed of one or more of B₂O₃, Al₂O₃, ZrO₂,Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, ZnO, La₂O₃, Nb₂O₅, TiO₂, HfO, andSb₂O₃.

With continued reference to FIG. 11A, the etch mask 1012 may be formedof a polymer (e.g., a carbon-based polymer), chromium, silicon oxide(SiO₂), or other material having sufficient stability and etchresistance for patterning the substrate 1010. In some embodiments, thepolymer may form a resist, e.g., a photoresist or imprint resist. Insome embodiments, the resist may be deposited by jet deposition. Asillustrated, the etch mask comprises a pattern formed of a plurality ofspaced-apart features 1013, which will be used to protect parts of theunderlying substrate 1010 from an etch, to define features in thatsubstrate 1010.

In some embodiments where the resist is a photoresist, the etch mask1012 may be patterned by exposure to light through a reticle. In someembodiments where the resist is an imprint resist, the etch mask 1012may be patterned by contact and imprinting with an imprint reticle. Insome other embodiments, the etch mask 1012 may itself be etched todefine the pattern of features in the etch mask. For example, a resist(not shown) may be provided over a layer of material (e.g., chromium,silicon oxide, etc.) for forming the etch mask 1012. The resist may bepatterned, e.g., by photolithography or imprinting, and then the patternin the resist may be transferred to a layer of material for forming theetch mask 1012, and the overlying resist may be removed, thereby leavingthe etch mask 1012.

With reference now to FIG. 11B, a cross-sectional side view of anexample of the structure of FIG. 11A undergoing a directional etch asillustrated. As illustrated, the etch mask 1012 may have a plurality offeatures 1013, with the features having a critical dimension of 1013 w.It will be appreciated that the critical dimension 1013 w may be thewidths of the features 1013, which may be elongated along a length axisout of the page. Preferably, the critical dimension 1013 w is largerthan the critical dimension 1014 w of the corresponding feature 1014 tobe etched in the underlying substrate 1010 using the etch mask features1013. In some embodiments, the critical dimension 1013 w may be selectedby identifying desired dimensional characteristics of first features(e.g., features 1016 (FIG. 11C)) to be formed in a high-index glasssubstrate 1010; identifying etching characteristics of an etchingprocess 1015 that is to be used for forming at least the first featuresin the high-index glass substrate; and determining, based on theidentified etching characteristics, biasing dimensional characteristicsof second features (e.g., features 1013) of a patterned layer (e.g.,etch mask 1012) to be formed on the high-index glass substrate. Forexample, the critical dimension 1013 w may be biased to be sufficientlylarger than the critical dimension 1014 w to compensate for etching ofthe etch mask 1012 by the particular etch chosen for etching thesubstrate 1010. Preferably, the sizes of the features 1013 aresufficiently large that, even when etched by the etch process 1015, themask features 1013 are of a size to form openings of a desired size inthe high-index glass substrate 1010. In addition, the heights of thefeatures 1013 are preferably also biased to compensate for the removalof material at the tops of the features 1013 by the etch.

As illustrated, the substrate 1010 may be etched by exposing thesubstrate to a directional etch through openings in the etch mask 1012.It will be appreciated that, in embodiments where the etch mask 1012does not have openings but has regions of lower thickness than thefeatures 1013, the regions of lower thickness will be removed by theetch, to subsequently leave openings that expose portions of thesubstrate 1010 to the etch. The directional etch 1015 may includevarious particles that contact the substrate 1010 to remove materialfrom that substrate. In some embodiments, the directional etch comprisesion beam milling. Advantageously, in some embodiments, the directionaletch can form an opening having a depth of about 50 nm or more in about20 seconds or less. In some embodiments, the directional etch can formthe opening having the depth of about 50 nm or more in about 10 secondsor less.

FIG. 11C illustrates a cross-sectional side view of an example of thestructure of FIG. 11B after etching the glass substrate 1010 andremoving the overlying etch mask 1012 (FIGS. 11A-11B). In someembodiments, the etch mask 1012 may be removed using an ashing processand/or a wet etch selected for the material forming the etch mask. Theetched substrate 1010 includes a plurality of features 1016 defined bythe etch 1015. The features have critical dimensions of 1016 w which maybe substantially equal to the desired critical dimensions 1014 w (FIG.11B).

As discussed herein, in some embodiments, the substrate 1010 may beutilized as a waveguide and the features 1016 may be optical elementsdefined in the surface of the waveguide. For example, the features 1016may form parts of the incoupling optical elements 1212, 1222, 1232, thelight distributing elements 1214, 1224, 1234, and/or the outcouplingoptical element 1250, 1252, 1254 of FIGS. 9A-9C.

As noted above regarding FIGS. 11A-11B, the features 1013 may be biasedto have sizes larger than the desired sizes of the features 1016ultimately patterned by the features 1013. This larger size may be setby patterning the layer forming the etch mask 1012 and providing a layerhaving the desired thickness for the etch mask 1012. In some otherembodiments, the features in the etch mask may be augmented to increasetheir size. FIGS. 12A-12D illustrate a process for etching features inthe substrate using an augmented etch mask.

With reference now to FIG. 12A, a cross-sectional side view isillustrated of an example of an etch mask 1012 overlying ahigh-refractive index glass substrate 1010. The etch mask 1012 comprisesfeatures 1013 having critical dimension 1013 w. It will be appreciatedthat the structure shown in FIG. 12A is similar to that shown in FIG.11A, except for the critical dimension 1013 w, which may be smaller thanthat of FIG. 11A.

The etch mask 1012 of FIG. 12A may be considered an initial etch maskand the dimensions of the features 1013 of that etch mask maysubsequently be increased. FIG. 12B illustrates a cross-sectional sideview of an example of the structure of FIG. 12A after expanding thesizes of features 1013 of the etch mask 1012. In some embodiments, thesize expansion may be achieved by depositing a conformal layer 1018 overthe etch mask 1012, thereby forming etch mask 1012′ having features1013′ with critical dimensions 1013 w′. For example, the conformal layer1018 may be a silicon oxide layer deposited by a vapor depositionprocess such as atomic layer deposition (ALD) or chemical vapordeposition (CVD). In some other embodiments, the sizes of features 1013(FIG. 12A) in the etch mask 1012 may be expanded by chemically reactingthe etch mask to form materials occupying larger volume. For example,the etch mask 1012 may be oxidized to, e.g, form the layer 1018, therebyforming the etch mask 1012′ with the expanded features 1013′. In someembodiments, the chemical reaction may occur to such an extent that thelayer 1018 may extend through substantially the entirety of the etchmask 1012′.

With reference now to FIG. 12C, a cross-sectional side view isillustrated of an example of the structure of FIG. 12B undergoingdirectional etch 1015. It will be appreciated that FIG. 12C is similarto FIG. 12B, except that the etch mask comprises the layer 1018 and thedirectional etch 1015 is preferably selective for the material of thelayer 1018 relative to the substrate 1010. The etch mask 1012′ comprisesa plurality of features 1013′, with the features having a criticaldimension of 1013 w′, which is larger than the critical dimension 1014 wof the corresponding feature 1014 to be etched in the underlyingsubstrate 1010 using the etch mask 1012′. As discussed herein, in someembodiments, the directional etch comprises ion beam milling.Advantageously, in some embodiments, the directional etch can form anopening having a depth of about 50 nm or more in about 20 seconds orless, or in about 10 seconds or less.

FIG. 12D illustrates a cross-sectional side view of an example of thestructure of FIG. 12B after etching the glass substrate 1010 andremoving the overlying etch mask 1012′ (FIG. 12C). It will beappreciated that FIG. 12D is similar to FIG. 11C. For example, the etchmask 1012 may be removed using an ashing process and/or a wet etchselective for the material forming the etch mask. The etched substrate1010 includes a plurality of features 1016 defined by the etch 1015 andhaving critical dimensions of 1016 w which may be substantially equal tothe desired critical dimensions 1014 w (FIG. 11B).

In the foregoing specification, various specific embodiments have beendescribed. It will, however, be evident that various modifications andchanges may be made thereto without departing from the broader spiritand scope of the invention. The specification and drawings are,accordingly, to be regarded in an illustrative rather than restrictivesense.

Indeed, it will be appreciated that the systems and methods of thedisclosure each have several innovative aspects, no single one of whichis solely responsible or required for the desirable attributes disclosedherein. The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure.

Certain features that are described in this specification in the contextof separate embodiments also may be implemented in combination in asingle embodiment. Conversely, various features that are described inthe context of a single embodiment also may be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination may in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination. No single feature orgroup of features is necessary or indispensable to each and everyembodiment.

It will be appreciated that conditional language used herein, such as,among others, “can,” “could,” “might,” “may,” “e.g.,” and the like,unless specifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/or stepsare included or are to be performed in any particular embodiment. Theterms “comprising,” “including,” “having,” and the like are synonymousand are used inclusively, in an open-ended fashion, and do not excludeadditional elements, features, acts, operations, and so forth. Also, theterm “or” is used in its inclusive sense (and not in its exclusivesense) so that when used, for example, to connect a list of elements,the term “or” means one, some, or all of the elements in the list. Inaddition, the articles “a,” “an,” and “the” as used in this applicationand the appended claims are to be construed to mean “one or more” or “atleast one” unless specified otherwise. Similarly, while operations maybe depicted in the drawings in a particular order, it is to berecognized that such operations need not be performed in the particularorder shown or in sequential order, or that all illustrated operationsbe performed, to achieve desirable results. Further, the drawings mayschematically depict one more example processes in the form of aflowchart. However, other operations that are not depicted may beincorporated in the example methods and processes that are schematicallyillustrated. For example, one or more additional operations may beperformed before, after, simultaneously, or between any of theillustrated operations. Additionally, the operations may be rearrangedor reordered in other embodiments. In certain circumstances,multitasking and parallel processing may be advantageous. Moreover, theseparation of various system components in the embodiments describedabove should not be understood as requiring such separation in allembodiments, and it should be understood that the described programcomponents and systems may generally be integrated together in a singlesoftware product or packaged into multiple software products.Additionally, other embodiments are within the scope of the followingclaims. In some cases, the actions recited in the claims may beperformed in a different order and still achieve desirable results.

Accordingly, the claims are not intended to be limited to theembodiments shown herein, but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein.

What is claimed is:
 1. A method for forming one or more diffractivegratings in a waveguide, the method comprising: providing a waveguidehaving a refractive index of greater than or equal to about 1.65,wherein more than 50 wt % of the waveguide is formed of one or more ofB₂O₃, Al₂O₃, ZrO₂, Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, ZnO, La₂O₃,Nb₂O₅, TiO₂, HfO, and Sb₂O₃; providing a mask layer over the waveguide,the mask layer having a pattern corresponding to the one or morediffractive gratings, the pattern selectively exposing portions of thewaveguide; and anisotropically etching the exposed portions of thewaveguide to define the one or more diffractive gratings in thewaveguide.
 2. The method of claim 1, wherein providing a mask layercomprises providing the pattern comprising a first diffraction gratingpattern over a first region and a second diffraction grating pattern inthe second region of the waveguide, wherein the second region extendsover a majority of an area of a surface of the waveguide.
 3. The methodof claim 2, wherein the first diffraction grating pattern corresponds toan incoupling optical element and the second diffraction grating patterncorresponds to an outcoupling optical element.
 4. The method of claim 3,wherein providing a mask layer comprises providing the patterncomprising a third diffraction grating pattern over a third region ofthe waveguide, wherein the third diffraction grating pattern correspondsto an orthogonal pupil expander configured to redirect light from theincoupling optical element to a top coupling optical element.
 5. Themethod of claim 1, wherein each of the one or more diffractive gratingscomprise substantially parallel lines, wherein each line has a criticaldimension of less than about 1 micron and an aspect ratio of betweenabout 1:10 to about 10:1.
 6. The method of claim 5, wherein each linehas a critical dimension of less than about 300 nm.
 7. The method ofclaim 5, wherein the mask layer comprises an underlying mask layer andan overlying conformal layer of mask layer material.
 8. A plasma etchingprocess for forming features in a high refractive index glass substrate,the process comprising: providing a patterned mask layer on at least aportion of the high refractive index glass substrate, the substrateformed of glass having a refractive index of greater than or equal toabout 1.65 and comprising less than about 50 wt % SiO₂, and etching thefeatures in the substrate by exposing the mask layer and high refractiveindex glass substrate to a plasma etch comprising chemical and physicaletchant species to selectively remove exposed high refractive indexglass from the high refractive index glass substrate.
 9. The plasmaetching process of claim 8, wherein the high refractive index glasssubstrate comprises less than about 30 wt % SiO₂.
 10. The plasma etchingprocess of claim 8, wherein more than 50 wt % of the high refractiveindex glass substrate is formed of one or more of B₂O₃, Al₂O₃, ZrO₂,Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, ZnO, La₂O₃, Nb₂O₅, TiO₂, HfO, andSb₂O₃.
 11. The plasma etching process of claim 8, wherein the highrefractive index glass substrate has a refractive index of greater thanor equal to about 1.70.
 12. The plasma etching process of claim 8,wherein exposing the mask layer and high refractive index glasssubstrate to a plasma etch comprises anisotropically removing highrefractive index glass from an exposed surface of the high refractiveindex glass substrate.
 13. The plasma etching process of claim 8,wherein the plasma is produced from a source gas and wherein the plasmais generated in situ in a reaction chamber accommodating the highrefractive index glass substrate.
 14. The plasma etching process ofclaim 13, wherein the source gas comprises SF₆ and Ar gas.
 15. Theplasma etching process of claim 13, wherein the source gas comprisesBCl₃, HBr, and Ar gas.
 16. The plasma etching process of claim 13,wherein the source gas comprises CF₄, CHF₃, and Ar gas.
 17. The plasmaetching process of claim 8, wherein the plasma etching process takesplace within a reaction chamber of an inductively coupled plasma (ICP)reactor.
 18. The plasm etching process of claim 17, wherein the ICPreactor is a dual frequency ICP reactor.
 19. The plasma etching processof claim 8, wherein each of the features has a critical dimension ofless than about 100 nm.
 20. The plasma etching process of claim 19,wherein each of the features has an aspect ratio of between about 1:10to about 10:1.
 21. The plasma etching process of claim 19, wherein thefeatures are sized and spaced to form a diffractive grating.
 22. Theplasma etching process of claim 8, wherein the mask layer comprises apolymeric resist layer.
 23. The plasma etching process of claim 8,further comprising removing remaining mask layer from the highrefractive index glass substrate after exposing the mask layer and highrefractive index glass substrate to the plasma.
 24. A process forforming features in a high refractive index glass substrate, the processcomprising: selectively exposing a portion of the high refractive indexglass substrate to a plasma in a reaction chamber to selectively removehigh refractive index glass from the high refractive index glasssubstrate; wherein the high refractive index glass substrate comprisesless than about 50 wt % SiO₂ and has a refractive index of greater thanor equal to about 1.65.
 25. The process of claim 24, wherein the highrefractive index glass substrate comprises one or more of B₂O₃, Al₂O₃,ZrO₂, Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, ZnO, La₂O₃, Nb₂O₅, TiO₂, HfO,and Sb₂O₃.
 26. The process of claim 24, wherein selectively exposing aportion of the high refractive index glass substrate defines a patternof protrusions in the substrate, wherein the protrusions form an opticaldiffraction grating.
 27. The process of claim 26, further comprisingdepositing a mask layer on the substrate; patterning the mask layer todefine a first set of spaced apart lines in a first region over thesubstrate, and a second set of spaced part lines in a second region overthe substrate, wherein selectively exposing a portion of the highrefractive index glass substrate comprises etching the substrate throughthe mask layer to form: a light incoupling diffractive grating in anarea of the substrate corresponding to the first region, and a lightoutcoupling diffractive grating in an area of the substratecorresponding to the second region.
 28. The process of claim 27, whereinpatterning the mask layer further defines a third set of spaced apartlines in a third region over the substrate, and wherein selectivelyexposing a portion of the high refractive index glass substratecomprises etching the substrate through the mask layer to form anorthogonal pupil expander corresponding to the third region.